Interaction of Glyceraldehyde-3-Phosphate Dehydrogenase With Isolated Microsomal Subfractions of Skeletal Muscle

A protein of subunit M _r 34,000 (corrected here and subsequently to 36,000) has been isolated from a muscle homogenate which catalyzes the formation of the triad junction from isolated transverse tubules and terminal cisternae. This protein is identified as glyceraldehyde-3-phosphate dehydrogenase on the basis of N-terminal amino acid sequence, amino acid composition, and enzymic activity. The oxidation of glyceraldehyde phosphate by the enzyme is slowly but progressively inhibited by terminal cisternae, longitudinal reticulum, and transverse tubules. Addition of Triton X-100 to terminal cisternae markedly enhances and accelerates the inhibition. Two distinct constituents of microsomes exhibit a progressive inhibition. One component has been fractionated on a hydroxyapatite column and was identified as calsequestrin. Calsequestrin reveals an immediate inhibition of glyceraldehyde phosphate oxidation which can be reversed by concentrations of CaCl ₂ below millimolar levels or by high ionic strength. Isolated terminal cisternae contain glyceraldehyde-phosphate dehydrogenase which can be extracted by high ionic strength.